92 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 54 



The ratios deduced from analyses of zinc bromide by Richards and 



Rogers are — 



2Ag:ZnBr,: : 100 -.104.380, ± .0007 

 2AgBr:ZnBr2: : 100: 59.962, ± .0004 



Hence Ag: Br:: 100: 74.077, ±.0016. 



Analyses by Baxter of ferrous bromide yield the following ratios : 



2Ag:FeBr,: : 100: 99.960, ± .0027 

 2AgBr:FeBr2: : 100: 57.4195, ± .00044 



Hence Ag: Br :: 100 : 74.087, ±.0049. 



Richards and Mueller studied potassium bromide with the subjoined 



results : 



Ag:KBr: :100:110.319, ± :0004 

 AgBr:KBr: : 100: 63.3727, ± .0003 



Hence Ag: Br :: 100 : 74.981, ±.0012. 



The combination of all these estimates is as follows : 



Richards, Sr series 74.077, ± .0024 



Richards and Rogers, Zn series 74.077, ± .0016 



Cooke, Sb series 74.078, ± .0219 



Richards and Mueller, K series 74.081, ± .0012 



Huntington. Cd series 74.086, ± .0098 



Baxter, Fe series 74.087, ± .0049 



General mean 74.0795, ± .00098 



Finally, combining the three groups of figures for the ratio Ag : Br : : 



100 : X we have — 



Direct determinations 74.0797, ± .00035 



Incidental determinations 74.082, ± .0006 



Indirect determinations 74.0795, ± .00098 



General mean 74.0802, ± .00029 



Addenda. The determinations by Archibald of the atomic weight 

 of platinum give the following ratios: 



Ag:Pt: : 100: 180.965, ± .0034 

 AgBr:Pt: : 100: 103.955, ± .0037 



Hence Ag : Br : : 100 : 74.080, ± .0070. 



From the work of Thorpe and Francis on strontium bromide we have — 



2Ag:SrBr„: : 100: 114.703, ± .0040 

 2AgBr:SrBr„: : 100: 65.892, ± .0011 



Hence Ag : Br : : 100 : ^74.077, ± .0067. 



